High temperature fuel cell generators employing interconnected, tubular fuel cells, with solid electrolytes, are taught by A. O. Isenberg, in U.S. Pat. No. 4,395,468. Fuel electrode, air electrode, solid electrolyte and interconnection configurations for individual fuel cells, are taught by A. O. Isenberg, in U.S. Pat. No. 4,490,444. Usually, a porous support tube of calcia stabilized zirconia, approximately 1 millimeter to 2 millimeters thick, has an air electrode deposited on it. The air electrode is from about 50 microns to 1000 microns thick (0.05 millimeter to 1 millimeter) and may be made of doped and undoped oxides or mixtures of oxides, such as LaMnO.sub.3, CaMnO.sub.3, LaNiO.sub.3, LaCoO.sub.3, LaCrO.sub.3, etc. Surrounding part of the outer periphery of the air electrode is a layer of gas-tight solid electrolyte, usually yttria stabilized zirconia, approximately 1 micron to 100 microns (0.001 millimeter to 0.1 millimeter) thick.
A selected radial segment of the air electrode not covered by electrolyte is covered by an interconnect material. The interconnect material is made of a lanthanum chromite film, of approximately 30 microns to 100 microns (0.03 millimeter to 0.1 millimeter) thickness. The synthesis of lanthanum chromite generally, is described by Alexandrov et al., in U.S. Pat. No. 4,035,266. The lanthanum chromite, for fuel cell interconnect application, is doped with one of calcium, strontium, or magnesium. Substantially surrounding the solid electrolyte is a second porous electrode which will be contacted with fuel during cell operation. This electrode is usually a nickel-zirconia or cobalt-zirconia cermet material. Deposited over the interconnect but not contacting the fuel electrode is a layer comprised of the same material as the fuel electrode.
The typical operating temperature of the solid oxide electrolyte fuel cell is from about 800.degree. C. to about 1200.degree. C. These fuel cells must be able to withstand occasional thermal cycling between about 25.degree. C. and their maximum 1200.degree. C. operating temperature. During these thermal cycles, all of the components must have a close match of thermal expansion characteristics in order to eliminate mechanical stresses, which can cause component layer cracking, with resultant leakage of oxygen and/or fuel and degradation of electrical characteristics of the cell. The components must also remain intact at the temperatures required during fuel cell fabrication, which may be as high as 1600.degree. C. It has been found that the thermal expansion match of the solid electrolyte or mixed oxide electrode materials with the interconnect could be improved. Any change, however, must not reduce the electrical conductivity and ion transfer rates in the cell.